Chromosome no. 1 of Crepis capillaris shows defined 3D-shapes in mitotic prophase.

The shape of mitotic prophase chromosomes has been studied in root tip nuclei by confocal microscopy and 3D-image analysis. Crepis capillaris chromosome no. 1 was used as a test object. Chromosome conformation was studied in early, mid- and in late prophase. In mid- and late prophase, individual chromosomes could be distinguished on the basis of their length. Early prophase chromosomes could not be distinguished as individuals. The central axes of prophase chromosomes were traced with an automated computer procedure and then represented as a string of 3D coordinates. This representation facilitated measurement along the chromosome axis of shape parameters such as curvature (amount of bending), torsion (helical winding) and torsion sign (helical handedness). Stretches of early prophase chromosomes showed full helical turns, which could be left- or right-handed. In the later prophase stages curvature and torsion were statistically analysed. Our data on 40 midprophase chromosomes no. 1 show that they are still highly curved, but full helical turns were no longer found. Instead, an overall meandering pattern was observed. In late prophase, one central loop persisted, flanked by two preferential regions of high curvature.

Detection of moving objects in video using a robust motion similarity measure.

This correspondence deals with the segmentation of a video clip into independently moving visual objects. This is an important step in structuring video data for storage in digital libraries. The method follows a bottom-up approach. The major contribution is a new well-founded measure for motion similarity leading to a robust method for merging regions. The improvements with respect to existing methods have been confirmed by experimental results.

Classification of organelle trajectories using region-based curve analysis.

A method based on analysis of the region of movement and the functioning of the acto-myosin cytoskeleton has been elaborated to quantify and classify patterns of organelle movement in tobacco pollen tubes. The trajectory was dilated to the region of movement, which was then reduced to give a one-pixel-wide skeleton, represented by a graph structure. The longest line in this skeleton was hypothesized to represent the basic track of the organelle along a single actin filament. Quantitative features were derived from the graph structure, direction of movement on the longest skeletal line, and distance between skeletal line and particle. These features corresponded to biological events like the amount of linear movement or the probability of attachment of an organelle to the actin filament. From 81 analyzed organelle trajectories, 17 had completely linear, 17 had completely non-linear, and 47 had alternating linear and non-linear movement. Selected features were employed for classification and ranking of the movement patterns of a representative sample of the population of organelles moving in the cell tip. The presented methods can be applied to any field where analysis and classification of particle motion are intended.